A hairy business—Periostracal hair formation in two species of helicoid snails (Gastropoda,Stylommatophora, Helicoidea)

In molluscs, the calcareous shell is covered externally by a thin organic layer, the periostracum. The periostracum of some pulmonate species is of special taxonomic interest because it bears distinct microscale architectures. Where and how these structures are formed is as yet unknown. Using histological sections through their shells, gelatin cuts, and live observations I studied the pattern by which the periostracal hair‐like projections in two helicoid land snail species are secreted and evenly arranged on the shell. The results indicate a complex mechanism: a hair is formed in the periostracal groove independently of the periostracum, after which it is attached to the edge of the shell, drawn out of the tissue, and finally swivelled to the upper side of the periostracum. Upon further growth of the periostracum, the hairs are finally fixed upright on the shell. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Ecohydrology of the Venezuelan páramo: water balance of a high Andean watershed

ABSTRACT

Background: The páramo provides key ecosystem services, including regulation and provision of water. To understand the underlying functions, an ecosystem approach is necessary.

Aims: We quantified the combined effect of vegetation and soils (integrated topographic and vegetation units – TVU) on the hydrological balance of a Venezuelan páramo micro-watershed and analyse its hydrological response to intra- and interannual rainfall variability.

Methods: Data (2008–2016) from meteorological stations of TVUs and of a streamflow station was used to calculate watershed level hydrologic balances. We quantified the impact of the TVUs outputs by calculating evapotranspiration under non-standard conditions (ETc adj).

Result: Evapotranspiration of wetlands and tarns was high, exceeding annual precipitation. Shrubland had low evapotranspiration. Recharge of páramo reservoirs (soils, wetlands, tarns) occurred when monthly rainfall exceeded 90 mm. In dry years there were lower water yields with less effective hydrological regulation. In average years the differences between input and output in watershed balances were very small.

Conclusions: The high and constant evapotranspiration of the wetlands and tarns (due to permanent water availability) suggests they could maintain streamflow during dry periods. Their high evapotranspiration rates are compensated by low rates in shrublands units, reducing the mean total evapotranspiration of the watershed. The watershed balances suggest a limited regulatory capacity in these relatively dry páramos with no volcanic soils.     

海南岛霸王岭热带云雾林雨季的环境特征

以海南岛霸王岭热带云雾林中热带山地常绿林和热带山顶矮林群落为对象, 分析了热带云雾林雨季光照、空气湿度、空气温度、土壤和地形特征, 为分析生物多样性、生态系统功能及其对气候变化的反应等生态学过程奠定基础。结果表明: 热带山地常绿林和热带山顶矮林在一天中的光合有效辐射呈单峰曲线变化, 热带山地常绿林各时段的光合有效辐射显著低于热带山顶矮林; 5-10月两群落类型日平均空气温度分别为(21.76 ± 2.44) ℃和(19.33 ± 1.03) ℃, 且随时间变化呈单峰曲线, 热带山地常绿林日平均空气温度显著高于热带山顶矮林; 5-10月两群落类型日平均空气相对湿度分别为(88.44 ± 2.90)%和(97.71 ± 0.80)%, 且随时间变化呈倒“S”型曲线, 热带山地常绿林各月日平均空气相对湿度显著小于热带山顶矮林; 与热带山顶矮林相比, 热带山地常绿林的土壤全氮、全磷、速效氮、有机质、pH和土壤厚度显著大, 而全钾和有效磷含量显著低; 热带山地常绿林的坡度、岩石裸露比例和海拔高度显著小于热带山顶矮林, 地形因子与其他生态因子显著相关; 主成分和相关性分析表明: 空气温度、有效磷、全钾、全氮及地形因子对热带云雾林植被分布有重要影响。     

On the Cytology and Fine Structure of the Neogregarine Syncystis aeshnae Tuzet and Manier, 1953 (Apicomplexa, Syncystidae)

The neogregarine Syncystis aeshnae Tuzet and Manier, 1953, was obtained from two species of dragonfly larvae, Aeshna grandis and Libellula quadrimaculata , collected in southern Sweden. Merogony, gamogony, and sporogony were observed in the adipose tissue, which was destroyed, and the haemocoele. Merozoites had a traditional apical complex. Gamonts associated in pairs did not unite conoid-to-conoid, and the border between gamonts was not found to break down. Each association produced 32 spores in bilobed gametocysts. Spores were elongate, oval, 4.0–5.8 × 8.0–10.0 μm in fixed and stained condition, each with 4+4 terminal and four equatorial thread-like projections. The thick-walled spore is considered the sporocyst. Species identification, ultrastructural cytology, and problems associated with using the terms "oocyst" and "sporocyst" are discussed.     

黄水河小流域土壤养分分布及其与地形的关系

基于GIS和地统计学原理,对丹江口水库水源区黄水河小流域土壤养分空间分布及其与地形因子间的关系进行分析.结果表明： 研究区土壤全氮、全磷、有机质的变异系数分别为51%、66%和85%,为中等变异,土壤速效磷的变异系数为161%,属强变异;土壤全氮和有机质表现为显著正向空间自相关,速效磷和全磷的空间自相关性较弱;海拔是影响该区土壤养分分布的主要因素,其对全氮、全磷和有机质都具有极显著影响,坡度和剖面曲率显著影响全氮和有机质分布.建立了地形因子与土壤养分含量空间分布的回归预测方程,并进行了数字化制图输出,为研究区土壤资源的精确管理提供了数据支持.     

Effects of past and projected river discharge variability on freshwater production in an anadromous fish

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Integrating future scenario‐based crop expansion and crop conditions to map switchgrass biofuel potential in eastern Nebraska,USA

Switchgrass (Panicum virgatum) has been evaluated as one potential source for cellulosic biofuel feedstocks. Planting switchgrass in marginal croplands and waterway buffers can reduce soil erosion, improve water quality, and improve regional ecosystem services (i.e. it serves as a potential carbon sink). In previous studies, we mapped high risk marginal croplands and highly erodible cropland buffers that are potentially suitable for switchgrass development, which would improve ecosystem services and minimally impact food production. In this study, we advance our previous study results and integrate future crop expansion information to develop a switchgrass biofuel potential ensemble map for current and future croplands in eastern Nebraska. The switchgrass biomass productivity and carbon benefits (i.e. NEP: net ecosystem production) for the identified biofuel potential ensemble areas were quantified. The future scenario‐based (‘A1B’) land use and land cover map for 2050, the US Geological Survey crop type and Compound Topographic Index (CTI) maps, and long‐term (1981–2010) averaged annual precipitation data were used to identify future crop expansion regions that are suitable for switchgrass development. Results show that 2528 km² of future crop expansion regions (~3.6% of the study area) are potentially suitable for switchgrass development. The total estimated biofuel potential ensemble area (including cropland buffers, marginal croplands, and future crop expansion regions) is 4232 km² (~6% of the study area), potentially producing 3.52 million metric tons of switchgrass biomass per year. Converting biofuel ensemble regions to switchgrass leads to potential carbon sinks (the total NEP for biofuel potential areas is 0.45 million metric tons C) and is environmentally sustainable. Results from this study improve our understanding of environmental conditions and ecosystem services of current and future cropland systems in eastern Nebraska and provide useful information to land managers to make land use decisions regarding switchgrass development.     

Modeling neolithic dispersal in central Europe: demographic implications

On the basis of new examination of ancient DNA and craniometric analyses, Neolithic dispersal in Central Europe has been recently explained as reflecting colonization or at least a major influx of near eastern farmers. Given the fact that Neolithic dispersal in Central Europe was very rapid and extended into a large area, colonization would have to be associated with high population growth and fertility rates of an expanding Neolithic population. We built three demographic models to test whether the growth and fertility rates of Neolithic farmers were high enough to allow them to colonize Central Europe without admixture with foragers. The principle of the models is based on stochastic population projections. Our results demonstrate that colonization is an unlikely explanation for the Neolithic dispersal in Central Europe, as the majority of fertility and growth rate estimates obtained in all three models are higher than levels expected in the early Neolithic population. On the basis of our models, we derived that colonization would be possible only if (1) more than 37% of women survived to mean age at childbearing, (2) Neolithic expansion in Central Europe lasted more than 150 years, and (3) the population of farmers grew in the entire settled area. These settings, however, represent very favorable demographic conditions that seem unlikely given current archaeological and demographic evidence. Therefore, our results support the view that Neolithic dispersal in Central Europe involved admixture of expanding farmers with local foragers. We estimate that the admixture contribution from foragers may have been between 55% and 72%.     

The topological organization of primary afferents in the terminal ganglion of crayfish,Procambarus clarkii

Summary The central projections of primary afferents in the terminal ganglion of the crayfish can be seen when an axonal filling with nickel chloride with subsequent silver intensification was used for identification. We describe here the topological relationships of the projections to the landmark structures of the neuropil.The terminal ganglion has five pairs of sensory nerves associated with the mechanosensory hairs and internal proprioceptors. The projection fields of the primary sensory neurons in the nerves Rl and R2 are almost entirely restricted to the ipsilateral half of the ganglion, whereas those of the nerves R3, R4 and R5 cross the midline to form three sensory commissures, A6SCI, A7SCI and A7SCII. The projection fields are segregated from each other, although all are restricted to the ventral neuropil which lies under the ventral intermediate tract (VIT). The intersegmental projections that ascend via the connective ipsilateral to their origins could be observed. This pattern of projection correlates well with the receptive fields exhibited by several mechanosensory interneurons on the body surface of the final segment.     

The morphological categorization of developing synaptic junctions

Summary The molecular layer of rat occipital cortex was studied at a number of ages throughout postnatal development in an attempt to formulate a quantitative morphogenetic scheme of synaptic development. As previous work had pointed to the potential usefulness of E-PTA stained material in synaptogenic studies, this technique was employed. Synaptic junctions were assigned to five categories, A-E, on the basis of variations in the organization of their presynaptic densities. Of these categories, Type A represented a mature junctional form with well-defined and discrete dense projections. Type E, by contrast, represented the immature end of the spectrum, its presynaptic apposition generally lacking recognizable densities. Types B-D represented intermediate forms.As development proceeded, the percentage of A type junctions increased from 0.3% at 7 days to 25% in the adult. Type E junctions showed the opposite trend falling from 42% at 7 days to 5% in the adult. On the basis of these results, and those relating to types B-D, possible morphogenetic schemes involving the five synaptic categories are put forward. These schemes incorporate and extend those previously suggested by other workers. By placing observations on a quantitative footing, the schemes proposed here lend themselves to use in experimental investigations.This work was supported by the Nuffield Foundation. We wish to thank Mr. W. Kendrick for technical assistance